Purging is an important procedure which is often overlooked in many gas processes. A method of purging, known as pressure cycle purging, is used on complex systems with dead end passages where a steady flow of inert gas cannot flush all areas of the system. Pressure cycle purging is normally accomplished using an inert purge gas such as clean extra dry nitrogen. Before initial and subsequent system startups, purging should be done to remove contaminants (such as air and water vapor) from the gas delivery system. To enhance operator safety, purging should also be performed before changing out cylinders to protect operators from exposure of corrosive or toxic gases.
Oxygen and moisture can adversely affect many applications, potentially reducing the quality of products being produced, or affecting the results of tests being performed. After cylinder connection, contamination from atmospheric air and water vapor (moisture) may adversely affect many applications (inaccurate processes, reduce HCL response, etc.); reduce the quality of the calibration gas (inaccurate control measurements, slow cycle—calibration times); affect the results of tests being performed; react with gases to form highly corrosive acids that react with most metals including stainless steel, thereby reducing service life of gas handling and application equipment (safety, repair and maintenance issues may be encountered); and/or react with iron and HCL to form iron oxide (rust).
Superior equipment design with the use of robust materials of construction and purging techniques will help avoid and eliminate these and other related problems from occurring. There is a need in the industry for a sample system incorporating proper purging methods for the sampling of reactive gases used in highly sensitive calibration and analysis applications